Assessment of pressure wave reflection: getting the timing right!

Abstract

Assessment of timing and magnitude of wave reflection is ideally based on wave separation analysis (WSA). In clinical practice, however, waveform analysis (WFA) is often used to study wave reflection, with different coexisting approaches to assess ‘landmarks’ on the waveform which are indicative for return of the reflected wave. The aim of this work was to compare WSA and WFA. Data were obtained from 2132 subjects (1093 women) aged between 35 and 56 and free from overt cardiovascular disease. Carotid pressure and aortic flow waveforms, and carotid-femoral pulse wave velocity were measured non-invasively. WSA yielded the timing of return of reflected wave (Tf-b), the ratio of forward and backward pressure wave (Pb/Pf), and the effective length of the arterial tree (Leff). WFA resulted in identification of the shoulder (Tsho) or inflection point (Tinf) as landmark points, with subsequently derived augmentation index and Leff (AIxsho and Leff,sho, AIxinf and Leff,inf, respectively). (i) Neither Tinf nor Tsho corresponded with the timing obtained from WSA. (ii) Measurements of Leff were found to decrease with age (conforming with current physiological insights) whilst Leff,inf was found to increase with age in women, and mixed results were obtained for Leff,sho. (iii) Both AIxinf and AIxsho showed a persistent gender difference which was not present in Pb/Pf. Using the pressure at Tf-b to calculate AIx, the systematic gender difference in AIxf-b was greatly reduced. Analysis of pressure wave reflection is optimally based on measurement of pressure and flow, rather than on waveform analysis alone.